#pragma GCC optimize(2)
#include <iostream>
#include <algorithm>
#include <cstring>
#include <string>
#include <map>
#include <vector>
 
using namespace std;
using LL = long long;
const int N = 110;
 
int n, index;
char str[N];
char res[N];
 
int main(){
 
 
    int T;
 
    scanf("%d", &T);
    while(T--){
        scanf("%d%s", &n, str + 1);
  
        index = 0;
        for(int i = 1; i <= n; i ++){
            int x1 = str[i] - '0';
            if(x1 != 0){
                res[index ++] = char('a' + x1 - 1);
            }else{
                if(i + 1 <= n && str[i + 1] == '0'){
                    int x2 = str[i - 1] - '0';
                    index -= 1;
                    res[index ++] = char('a' + x2 * 10 - 1);
                    i ++;
                }else{
                    index -= 2;
                    int x2 = str[i - 1] - '0';
                    int x3 = str[i - 2] - '0';
                    res[index ++] = char('a' + x3 * 10 + x2 - 1);
                }
            }
        }
 
        for(int i = 0; i < index; i ++){
            printf("%c", res[i]);
        }
        printf("\n");
        
    }
 
    return 0;
}